Method for separating hemicelluloses from a biomass containing hemicelluloses and biomass and hemicelluloses obtained by said method

ABSTRACT

The invention relates to a method for separating hemicelluloses from a biomass containing hemicelluloses. The method includes the steps of: a) extracting the hemicelluloses from the biomass containing hemicelluloses by treating them with a complex compound in an aqueous solution, and forming a soluble hemicellulose complex, and b) separating the complexed hemicelluloses from the biomass. The method is especially suitable for producing high-quality chemical conversion pulp from raw cellulose. The products produced with the method of the invention have a high degree of purity, and the method is extremely economical and causes few emissions. Hemicelluloses in a pure form can be obtained as by-products of the method.

The invention concerns a method to separate hemicelluloses fromhemicellulose-containing biomass as well as biomass and hemicelluloseobtained by this method.

In the case of celluloses one distinguishes between paper pulp, that inaddition to the main component of α-cellulose may contain hemicelluloseup to 25%, and higher grade dissolving pulp with an α-cellulosecomponent of above 90%, the hemicellulose component of which should notexceed a few percents. It is known that the dissolving pulp is one ofthe most important cost factors in the production of cellulose acetate,filter tow and other high-grade cellulose products. The highest demandsare placed on the dissolving pulp, serving as initial substance for theproduction of these cellulose products. Thus the α-cellulose content,particularly if a subsequent acetylation is intended, should, as a rule,be above 96%. These high-grade types of dissolving pulp are marketedonly by a few suppliers with less than 2% of market share of theworldwide pulp production.

For the production of such dissolving pulps from timber or a comparablebiomass in addition to the removal of the lignin an as far as possibleseparation of the hemicellulose is necessary, since timber is acomposite material with the basic components of cellulose, lignin andhemicellulose.

According to the state-of-the-art numerous methods have been developedfor the chemical decomposition and removal of hemicelluloses fromhemicellulose-containing biomasses. A classic method for the removal ofhemicelluloses is by the hydrolytic disintegrating process. In thisconjunction the treated material can be subjected to a hydrolyticdisintegration by, for example, bringing it into contact withsuperheated steam at elevated pressure. The decomposition of thehemicelluloses achieved on this occasion is, however, not selective,whereby a significant decomposition of the cellulose itself takes place.

A further possibility is the hydrolysis under acidic conditions. Thedecomposition of the hemicelluloses is not selective enough according tothis disintegration method either. A clear decrease of the viscosity isnoticed, that can be explained with a considerable decomposition of thecellulose. This decomposition of the cellulose takes place partlytogether with a deterioration of the whiteness. An improvement can beachieved by a downstream connected extraction of the pre-treated, withsteam or acid, pulp with alkaline media. By virtue of this somewhathigher α-cellulose contents can be achieved. But even with thispost-treatment the removal of the hemicelluloses is not sufficientlyselective. It is surprising, that this classic disintegrating method ofthe hemicelluloses with acids and bases turns out to be completelyuseless. The cause of this is presumably that in high-yield paper pulpsthe hemicelluloses precipitate partly again on the cellulose fibres. Inthis form the hemicelluloses are obviously more difficult todisintegrate hydrolytically than in the original raw material, timber.

A further known possibility to separate hemicelluloses fromhemicellulose-containing biomass is by selectively decomposing thehemicelluloses using suitable oxidative or reducing treatment and thusbring it to a soluble and, consequently, extractable form. The chemicalreactions taking place in this conjunction are similar to those whichare also used for the improvement of the pulp. On this occasiontypically oxidising agents, like urea nitrate, H₂O₂ and percarbamide inaqueous solution, partly under alkaline or acidic conditions, orreducing agents, like Na[BH₄] in water or methanol, for example, areused. By the oxidative decomposition with, for example, percarbamide, itis possible in principle to decompose hemicelluloses in the paper pulp.The range of high qualitative dissolving pulp with an α-cellulosecontent of above 96%, however, cannot be achieved without perceptible DPdecomposition of the cellulose. No sufficiently selective decompositionof the hemicelluloses without accompanying cellulose decomposition canbe achieved with this method either.

Consequently, the methods according to the state-of-the-art are eitherbased on expensive raw materials, particularly cotton linters, orrequire an elaborate management of the method, while, as a rule, thepulp is more or less damaged, resulting in a lowering of the degree ofpolymerisation (DP value), loss of accessability or reactivity and anundesirable colouring, for example during a subsequent acetylation. U.S.Pat. No. 5,876,779 concerns a method for the production of acellulose-containing grain extract. On this occasion plant fibres areextracted with a sodium hydroxide solution. The mixture obtained isacidified to precipitate a first hemicellulose fraction. A secondhemicellulose fraction is precipitated from the filtrated materialobtained by adding ethanol. The extract claimed is essentially analkaline-soluble complex of a hemicellulose mixture.

Having this background in mind, the object of the invention is toprovide a method for the separation of hemicelluloses fromhemicellulose-containing biomass, that avoids the disadvantages of theabove described method and makes it feasible to obtain high-grade pulpsin a simple and gentle manner. In particular the method should make aselective separation of the hemicelluloses from the cellulose-containingbiomass possible without a significant decomposition of the cellulose.Furthermore, the method should operate economically, i.e. costeffectively and not produce at all or produce only littleenvironmentally damaging emissions.

According to the invention this objective is achieved by a method toseparate hemicelluloses from hemicellulose-containing biomass by thefollowing steps:

-   -   a) extraction of the hemicelluloses from the        hemicellulose-containing biomass by treating it with a complex        compound in aqueous solution thus forming a soluble complex of        the hemicelluloses, wherein in step a) as complex compound a        coordination compound from a transition metal and a unidentate        or polydentate nitrogen-containing and/or oxygen-containing        ligands are used,    -   b) separation of the complexed hemicelluloses from the biomass.

Accordingly, the method according to the invention relates to theproduction of high-grade pulps with an α-cellulose proportion of approx.above 96% and a very small hemicellulose component. Therefore it makes ahighly selective separation of hemicelluloses from thehemicellulose-containing biomass under mild conditions in the form of anextraction possible, while no decomposition of the cellulose worthmentioning takes place.

Within the scope of the invention the biomass that can be used asinitial material in the method according to the invention is notsubjected to any limitation. Examples of preferred raw pulps are:coniferous wood sulphate, spruce sulphite, beech sulphite and eucalyptsulphate. Raw pulp, for example, represents a particularly suitableinitial substance for the method and thus can be purified to ahigh-grade dissolving pulp. Raw pulps, that have been obtained bydelignifying lignocellulose-containing biomass, particularly timber, arepreferred. The biomass is introduced preferably in a finely comminuted,particularly ground, form.

According to step a) of the method according to the invention a complexcompound is introduced into an aqueous solution that with thehemicelluloses forms soluble complexes and leaches them out of thebiomass. On this occasion coordination compounds from a transition metaland a unidentate or polydentate nitrogen-containing and/oroxygen-containing ligands are used. Particularly preferred transitionmetals are nickel, copper, cadmium, cobalt, palladium and/or zinc. Asligands polydentate nitrogen-containing ligands are preferred, inparticular tris(2-aminoethyl)amine, ethylene diamine and/or diethylenetriamine. According to an embodiment preferred by the invention ascomplex compound [Ni(tris(2-aminoethyl)amine) (OH)₂], described in thefollowing as “nitren”, is used, while “tren” designates the ligandstris(2-aminoethyl)amine.

The concentration of the complex compound in aqueous solution ispreferably in the range of approx. 0.1 to 10, in particular approx. 1 to3% by weight. If the value falls below 0.1% by weight, soluble complexesof the hemicellulose can no longer be formed. If a concentration of thecomplex compound in the aqueous solution exceeds 10% by weight, a markeddissolving of the cellulose may already occur, which is undesirable.

The extraction can be carried out in one or several stages, carried outpreferably in counter-current. The temperature during the extraction ispreferably in the range of approx. 0° C. to 90° C., particularly approx.10° C. to 80° C. and most particularly preferred approx. 20° C. to 40°C. The duration of the extraction is approx. 5 min to 16 hours,particularly approx. 15 min to 2 hours. The liquor ratio used during theextraction in a preferred embodiment is approx. 1:3 to 1:30, inparticular approx. 1:5 to 1:20, while within the scope of the inventionunder “liquor ratio” the ratio of the hemicellulose-containing biomass(in kg) to the aqueous solution of the complex compound (in L) isunderstood. The pH value during the extraction is preferably 10 to 14,in particular approx. 13 to 14.

The complexed hemicelluloses, present in the solution by virtue of thereaction with the complex compound, are separated afterwards in step b)from the remaining biomass modified by the method. The separation iscarried out preferably by filter presses. To enable the purification ofthe expressed biomass, modified by the method, from the adheringresidues of the complexed hemicelluloses, the biomass is appropriatelysubjected to one or several washing stages. The washing is preferablycarried out with water and/or an aqueous solution of a diluted acid,like acetic acid, a complex former for the transition metal, liketris(2-aminoethyl)amine, and/or ethanol amine, NaOH or ammonia. Washingwith an aqueous solution of ammonia with a concentration of approx. 0.5to 3%, in particular approx. 1%, has proved itself as particularlyadvantageous. To achieve an even more effective purification of thebiomass modified by the method, the washing step may be carried out alsoin the form of a Soxhlet extraction, for example with an approx. 0.5 to3% acetic acid. The pulp obtained thus can be directly used or furtherprocessed in the conventional manner, for example by derivatisation.

By lowering the pH value to below 10, in particular to approx. 5 to 3,the hemicelluloses can be precipitated from the separated solution ofthe complexed hemicelluloses. Due to the lowering of the pH value theOlat complexes formed become unstable, resulting in the precipitation ofthe hemicelluloses. After the precipitation the hemicelluloses can beisolated by, for example, filtration, and subsequently possibly washedonce or several times.

Subject matter of the invention is also the biomass modified by themethod and obtained by separating the hemicelluloses, that ischaracterised by a low residual contents of the hemicelluloses. Themodified biomass obtained in this manner preferably has a residualcontents of hemicelluloses of less than approx. 8%, particularly lessthan approx. 4%.

This invention further concerns also hemicelluloses obtainable by themethod according to the invention, xylan or galactomannan, for example.A particularly interesting product that is present when isolating thehemicelluloses, is xylan. Polymeric xylan is in particularly greatdemand by the pharmaceutical industry.

Xylan is used as raw material for the production of xylan polysulphate(pentosan polysulphate). Xylan polysulphate has a diverse activityspectrum, that is comparable with that of heparin. The continuouslyincreasing demand of such active substances cannot be satisfied bynatural heparin, so that substitute materials are being sought all thetime. Xylan polysulphate is used, for example, as antithrombotic agent,anticoagulant, for the lowering of the blood's fat contents, againstarthrosis, as immuno-stimulant (anti-AIDS, anti-tumour) and in furtherpharmaceutics with an extensive application in the indicated spectrum(e.g. TAVAN-SP 54®, FIBREZYM®, THROMBOCID®, KLISMACORT®, TACHOLIQUIN®,CARTOPHEN VET®, ELMIRON® and others). Therefore it becomes obvious thatthe hemicelluloses, that can be isolated according to the invention, areof great interest for industrial application.

A further factor to be considered after the completion of step b) of themethod is the residual contents of the transition metals, like nickel,for example, that by virtue of the complex compound passes into theprecipitated biomass, modified by the method, and the hemicelluloses. Ifthe contents in the products of the method of the transition metal istoo high for a desirable further processing, it is possible to reducethis by washing and/or treatment steps to a desirable level. In somecases it may be an advantage if the biomass, modified by the method andobtainable by the method according to the invention, has a contents ofthe transition metal in question below approx. 100 ppm, particularlybelow approx. 10 ppm, what can be achieved, for example, by appropriatewashing.

The economic consideration of the method according to the inventionleads altogether to very positive results. The economy stems from thefact that the hemicelluloses, present complexed in the solution, can beseparated without great expense from the biomass by simple steps of themethod. From the point of economics it is a particular advantage whenthe separated hemicelluloses precipitate particularly in the form ofxylans and mannans and thus represent a valuable by-product. Thereforethe method proves to be particularly effective for paper pulps with ahigh proportion of xylan, like eucalypt pulp (Cellbi of Bacell), forexample.

For a further improvement of the economics one can appropriately rely ontechnologies, like steam recompression or diaphragm separation, for therecovery or concentration of the complex compound used in the solution,so that the extracting agent can be reused and an economical managementwith a circulation is possible. One may start with cost-effective rawmaterials, like paper pulp, for example. The method leads to ahigh-grade dissolving pulp, in which the cellulose did not experienceany reduction of the DP by hydrolytic or oxidative decomposition.

A combination of the method according to the invention with knownmethods is also feasible. Thus the known delignifying process can beadvantageously combined with the method according to the invention intoan economically interesting total process. Thus a cost-effectivehigh-yield pulp can be delignified in a first stage (e.g. treatingspruce timber with ethanol amine), directly followed by the methodaccording to the invention as a second stage. By combining the twomethods energy can be saved, since additional intermediate stages forpurification or drying can be dispensed with. Furthermore, the normallyemployed pH exchange to disintegrate the hemicelluloses can be omitted.This means that losses of yield can be avoided and a lower cellulosedecomposition is achievable by combining the two methods.

The technical teaching according to the invention is further illustratedin the following based of the attached figures, while the invention isnot limited to the embodiments explained. Rather do further refinementswithin the scope of the teaching of the invention become familiar to theperson skilled in the art. The figures show in:

FIG. 1—the chemical formula of a complex compound that can be usedaccording to the invention for the extraction of hemicelluloses from thebiomass as well as their reaction of formation and reaction according tothe invention;

FIG. 2—a schematic illustration of a preferred embodiment of the methodaccording to the invention;

FIG. 3—a diagram of the residual nickel contents in the pulp orcellulose acetate after various stages of the washing/method, and

FIG. 4—a diagram of the residual nickel contents in xylan after variousstages of washing.

FIG. 1 shows an example of a complex compound for the extraction ofhemicelluloses from the hemicellulose-containing biomass according tostep a) of the method according to the invention. In this case one dealswith a coordination compound from a transition metal and a polydentatenitrogen-containing ligand, wherein the transition metal representsnickel. According to this example the polydentate nitrogen-containingligand is tris-(2-aminoethyl)amine and is obtained by reactingnickel(II)hydroxide with (tris(2-amino ethyl)amine in a 1:1 ratio ascomplex. Reaction (1) represents the formation of[Ni(tris(2-aminoethyl)amine) (OH)₂] (“nitren”). One deals here with adeep blue solution with a pH value of approx. 13 to 14. The complexforms relatively stable Olat complexes with dihydric alcohols, likesugar alcohols, for example. The complex formation of nitren withhemicelluloses is illustrated in reaction (2) in the example of xylan.

Due to the complex-forming properties the nitren is in the position todissolve the polysaccharides. The concentration of the nitren requiredfor this depends from the structure, i.e., inter alia, from the sugarbuilding blocks, the coupling, the length of the chain and the molecularweight of the polysaccharides. The concentration of the complex compoundin aqueous solution is advantageously in the range of approx. 0.1 to 10%by weight.

FIG. 2 shows a simplified diagram of a preferred embodiment of themethod according to the invention. In this case according to step a) thepulp to be extracted is reacted with the complex compound [Ni(tren)(OH)₂] (“nitren”) in a diluted aqueous 1–4% solution and intensivelymixed for some time. According to step b) it is filtered, washed with a0.4% sodium hydroxide and afterwards with water. Afterwards theextracted pulp, modified by the method and possibly after drying, can befurther processed, for example, by derivatisation. The blue filteredmatter is reacted with a little acid, due to which the pH value changesfrom 13 to 10. By virtue of this the hemicelluloses precipitate and canbe separated in a simple manner. By adding NaOH and thus raising the pHvalue from 10 to a pH value of 13 the extracting agent is regeneratedand can be returned into the circuit.

The described regulation of the pH may also be carried out via an ionexchanger. Thus, for example, the concentration of salts in theextraction circuit would be avoided, what could impair the properties ofthe extraction agent. The washing lyes, occurring during thepurification of the pulp, can be concentrated via an evaporator andreturned to the circuit. Thus the chemicals used in this version of theinvention are sodium hydroxide, acids or ion exchanger, while they areused altogether in considerably smaller quantities than in the knownalkaline extraction methods.

Based on a diagram FIG. 3 illustrates the residual nickel contents ofthe pulp or the cellulose acetate in accordance with the variouswashing/treatment steps. The invention has shown that it could be anadvantage to appropriately reduce the residual contents of thetransition metal from the complex compound used. Thus it is possible toremove the nitren residues from the pulp by an appropriate washing with,for example, water. The remaining contents of the transition metal canbe markedly reduced by further washing with diluted acids, like aceticacid. Thus, after expressing a filter cake with a solids contents ofapprox. 40% by mass and a nickel contents of 0.37 g Ni/kg of wet pulp,the nickel contents can be clearly reduced by Soxhlet extraction with 1%acetic acid to 0.029 g Ni/kg of the filter cake.

In addition, a counter-current wash can also be carried out to increasethe effectiveness of the washing process.

The adding of suitable displacing ligands, like an ammonia solution ordiluted sodium hydroxide, to the wash may also be considered, whichrelease the complex compound and the polysaccharide from the Olatcomplex.

A further possibility to lower the contents of the transition metals isby carrying out an exchange of the solvents. For example, a pulp with a0.37 g Ni/kg of filter cake is subjected after solvent exchange toacetylation in glacial acetic acid and saponification to 2,5-celluloseacetate. The cellulose acetate obtained had a residual nickel contentsof only 23 ppm.

To be used as a filter tow, the contents of the transition metal has tobe preferably reduced to below 10 ppm. This can be achieved, forexample, by precipitating the cellulose acetate, possibly obtaining aresidual contents of less than 1 ppm.

The individual treatment stages with the respective residual nickelcontents become obvious from FIG. 3.

FIG. 4 illustrates that also with regard to the separated hemicellulosesthere is the possibility to reduce the nickel contents to a desiredlevel by an appropriate post-treatment. Appropriately this is carriedout when a commercially utilisable quality of, for example xylan, isrequired. Thus washing with basic, displacing ligands give a clearlypositive effect. The efficiency of the nickel removal from, for example,xylan, increases for a 1% solution each with the sequence: ethanolamine<NaOH<ammonia<tris-(2-aminoethyl). As anticipated, thepost-treatment of a nickel-containing xylan precipitation with nitren inexcess is the most effective. There is also the possibility of thetreatment with a 1% ammonia solution, which is particularly advantageoussince due to its volatility the ammonia can easily be expelled andseparated from the strongly alkaline nitren solution.

The advantages associated with the invention are manifold: Thus themethod according to the invention with regard to the quantitative andqualitative conditions shows a surprising flexibility when compared withthe method according to the state-of-the-art outlined in theintroduction. Numerous pulps can be used as initial materials, making asimple access to dissolving pulps possible by removing thehemicelluloses. One can commence with cost-effective raw materials, likepaper pulp, for example. The paper pulp leads to a high-grade dissolvingpulp, in which the cellulose was not subjected to a reduction of the DPby hydrolytic or oxidative decomposition. Consequently, a sufficientlyselective and effective removal of the hemicellulose is possible in asimple manner without damaging the α-cellulose. Thus paper pulp (typicalα-cellulose contents approx. 81%) can be improved, without damaging thepulp (no cellulose decomposition), to become a dissolving pulp with aα-cellulose contents of above 96%. Moreover, the accessability andconsequently the reactivity of the pulp is increased in comparison withpulps produced according to the known methods.

In this manner highly purified dissolving pulps can be used for specialapplications, for example as linter substitute or for derivatives, whichrequire a particularly high degree of polymerisation and α-cellulosecontent, like cellulose ester, cellulose ether, cellulose nitrate, etc.,for example. According to the invention an improvement of the raw linterto linter pulp can also be carried out, what is of particular interestfrom the point of view of economics.

An essential advantage of the method according to the invention is thatapart from the simple execution in a few steps at room temperature oreven by cooling, the extracting agent can be reused by, for example,employing steam recompression or diaphragm separation, so that aneconomical management in the circulation is possible. By recovering thecomplex compound, its loss per process cycle can be adjusted to lessthan approx. 2%, so that the cost of the chemicals remain low. Due tothis the use of the method according to the invention is feasible on anindustrial scale.

After the separation of the solution containing the complexedhemicelluloses from the extracted biomass, modified by the method, thehemicelluloses in the form of, for example, xylans or galactomannans,can be isolated by precipitation almost quantitatively in polymeric formand thus further processed to a final product and used commercially. Thehemicelluloses represent valuable by-products of the method according tothe invention and are in great demand, for example, in pharmaceutics.

It is a further possibility to reduce, if necessary, the contents of thetransition metals in the products obtainable by the method to adesirable level by appropriate treatments, like washing and treatmentstages, so that no problems in this regard would arise during a furtherprocessing.

Moreover, the method described is suitable to be combined with otherknown methods, like for the separation of hemicelluloses from timberdelignified by ethanol amine extraction and can consequently beparticularly advantageously coupled with that method. By virtue of thissteps of the method can be dispensed with since a direct furtherprocessing is possible.

Due to the high efficiency, the low energy requirement and thepossibility of recovering, almost completely, the complex compound used,the method according to the invention is very economical andenvironmentally friendly at the same time.

In the following the invention is explained in detail based on examples,that should not limit the teaching according to the invention. Withinthe scope of the disclosure according to the invention furtherembodiments are obvious to the person skilled in the art.

EXAMPLES

The κ (kappa) number (lignin contents) stated in the following wascarried out based on the determination according to Zellcheming PamphletIV/37/80. In this conjunction the titration was carried out with 0.1 npotassium permanganate solution (3.161 g/L). The quantity in mL of 0.1 npotassium permanganate solution consumed for the hydration of 1 g ofpulp corresponds to the κ number. The lignin contents (in % of the pulp)can be estimated from the κ number by multiplying with 0.15.

Example 1 Composition of the Initial Pulps

Paper pulps of various manufacturers have been selected for theexperiments as initial substances. They differ with regard to the rawmaterials (types of timber) used as well as the disintegration andbleaching process. The corresponding analysis data are summarised inTables 1 to 3.

TABLE 1 Characterisation of the initial pulps Visco- κ ash SiO₂ DCM sityR Whiteness* number % % % mL/g 10% % ISO Spruce 1.58 0.24 <0.01 0.24 79586.15 87.5 sulphite ECF Eucalypt 0.96 <0.01 <0.01 0.07 904 94.84 89.2sulphite ECF *measured on the pulp sheet DCM - dichloromethane extractR10 - 10% extract with sodium hydroxide (see DIN 54355) ECF - bleachedfree of elementary chlorine

TABLE 2 Relative carbohydrate composition of the initial pulps GlucoseMannose Xylose Residue % % % % Spruce sulphite 85.74 6.96 7.72 0 ECFEucalypt sulphate 80.57 0 18.65 0 ECF The values are average values ofthree individual determinations.

TABLE 3 Metal contents of the initial pulps Mg Mn FE Cu Ca ppm ppm ppmppm ppm Spruce sulphite 98 352 1.0 34.6 0.6 ECF Eucalypt sulphate 129 740.3 4.8 0.6 Eucalypt sulphate 136 49 0.3 4.9 1.1 (after washed by water)Eucalypt sulphate 143 26 0.4 16.9 4.4 (after washed by water, ruffled)

Thus the selected pulps represent a wide selection of paper pulp typeswith various α-cellulose contents (approx. 80 to 89%) with variouscompositions of the hemicelluloses (xylan 4 to 19%, mannan 0 to 7%).There are, furthermore, depending from the method of manufacture, partlyconsiderable differences, particularly in the structure of the leavesand fibres, the residual lignin contents (κ number) as well as thedistribution of the hemicelluloses.

Various paths can be followed for the production of dissolving pulp frompaper pulp. Amongst these are the classic disintegration ofhemicelluloses with acids and bases as well as an oxidative or reductivedecomposition of the hemicelluloses. In the following some possibilitiesare described based on comparative examples.

Comparative Example 1 Hydrolytic Disintegration

For the hydrolysis without acidic or basic additives a steam treatmentwas carried out at 140° C. (p=3.6–3.7 bar) with treatment times of 20–80minutes on eucalypt pulp as an example. The R18 value (18% sodiumhydroxide; see DIN 54355) was reduced on this occasion from approx. 95%to 91.5%, and the viscosity, that is directly proportional to DP, from920 to 370 mL/g. The comparison with the analyses of the initial pulpwith approx. 80% α-cellulose contents shows that under these conditionsno selective decomposition of the hemicelluloses and a significantdecomposition of the cellulose takes place. Such a treatment of pulptypes under the conditions described is therefore extremelydisadvantageous.

Comparative Example 2 Disintegration under Acidic Conditions

The experiments of acidic hydrolysis of hemicellulose were carried outboth with glacial vinegar and diluted acetic acid (1%). The treatmentlasted 20–120 minutes at temperatures of 40–140° C. The hemicellulosesdid not decompose selectively enough according to this method ofdisintegration either. A clearer reduction of the viscosity is alreadynoted, that can be explained with a considerable decomposition of thecellulose. This decomposition of the cellulose takes place partly with adeterioration of the whiteness. The results are illustrated in Table 4.

TABLE 4 Disintegration of eucalypt sulphate paper pulp under acidicconditions Temp. Time Treatment ° C. min Yield % η mL/g R18 WhitenessUntreated — — 920 95 91.7 1% acetic acid 140 20 98.6 430 92.5 88.6 1%acetic acid 140 40 94.3 340 91.3 86.9 1% acetic acid 140 80 95.9 28090.0 85.1 Glacial vinegar 80 40 99.9 875 93.4 91.8 Glacial vinegar 14040 93.7 260 85.3 86.7

Comparison Example 3 Alkaline Extraction with Steam and Acid Treatment

Although by a downstream connected extraction of the pulps, treated withsteam or acid, somewhat higher α-cellulose contents of approx. above 90%are achieved, but even with this treatment the removal of hemicellulosesis not adequately selective or even complete in the case of any of thepulp specimens.

Example 2 Single-stage Extraction of Eucalypt Pulp

The suitability of the method according to the invention for a gentleseparation of hemicelluloses from raw pulp was investigated in theexample of the extraction from eucalypt pulp, using nitren. Theextraction is carried out with a 3% nitren solution at room temperatureover various periods of time. The results are shown in Table 5.

TABLE 5 Single-stage extraction of eucalypt pulp with a 3% nitrensolution at room temperature Period of α-cellulose treatment contents %nil 80.57 30 min 92.11 16 h 92.80

The results shown in Table 5 clearly show, that by extracting withnitren an efficient separation of the hemicelluloses is achieved whileproducing a pulp with a high α-cellulose content. It has been furthershown, that in the case of the eucalypt pulp used a prolongation of theperiod of extraction over 30 min does not bring any advantage with it.In the case of the periods investigated (30 min and 16 hours)practically no difference can be observed between the α-cellulosecontents achieved with the different extraction periods. The valuesobtained fluctuate within the error range of the method. It is, however,to be noted that when using plates of pulp (or roughly comminuted pulp)approx. 1 to 2 hours are necessary for a uniform wetting and swelling ofthe pulp, so that the extraction periods extend accordingly.

Under the conditions mentioned no cellulose decomposition could bemeasured. In a direct comparison after the nitren extraction limitviscosities higher than those in the untreated pulp could be measured.This could be explained foremost by the extraction of thehemicelluloses.

Example 3 Single- and Two-stage Extraction of Eucalypt Pulp

For purposes of comparison, in addition to the single-stage nitrenextraction a two-stage nitren extraction was also carried under the sameconditions as in Example 2. The results are shown in Table 6.

TABLE 6 Limit viscosities of eucalypt pulp with and without nitrentreatment Viscosity Eucalypt pulp (Cuen)* mL/g Untreated 840Single-stage nitren extraction 905 Two-stage nitren extraction 970 *Cuen(see DIN 54270)

The above viscosity values show that no cellulose decomposition takesplace at any of the extractions.

Example 4 Two-stage Extraction of Eucalypt Pulp and Spruce Sulphite Pulp

For the purposes of comparison in addition to eucalypt pulp sprucesulphite pulp (Paskov) was also subjected to a two-stage extraction witha 3% nitren solution at a liquor ratio of 1:10. The results are shown inTable 7.

TABLE 7 Two-stage extraction (liquor ratio 1:10) with 3% nitren solutionNo. of Temp. extraction Mannose Pulp ° C. stages Glucose % Xylose % %Eucalypt Untreated 80.57 18.65 0 sulphate Eucalypt 0 2 94.81 5.07 0.12sulphate Eucalypt 25 2 96.13 3.76 0.11 sulphate Spruce sulphiteUntreated 85.74 7.72 6.96 Spruce sulphite 25 2 95.04 0.46 4.50

The results with the spruce sulphite pulp show that nitren leachespreferably xylan from the paper pulps.

The thus dissolved hemicelluloses were precipitated from the nitrensolution by lowering the pH value. The precipitation commenced at pH 10and was complete at pH 4. According to the carbohydrate analysis in thecase of single-stage extraction an almost pure (approx. 99%) xylan wasobtained. After the two-stage extraction the precipitation obtains fromthe extract approx. 85% xylan and approx. 15% glucose. It needs to benoted, that the xylan obtained in this manner is free of the otherwiseusual brown colouring in the polymeric form.

Example 5 Balance of Nickel Based on a Single-stage Extraction of Pulpwith Subsequent Washing Steps.

In the following based on a tabulated summary a version of the methodaccording to the invention is illustrated in detail. Nitren was used ascomplex compound.

After the extraction it was expressed and washed twice with water andonce with 0.5% acetic acid.

Extraction (single-stage) Pulp C₀ Hemicelluloses Gross Moistureα-cellulose (xylan) 87 g 6.95% 65.2 g 15.0 g Nitren solution Solution,total Nitren, measured Ni, measured 869 g  2.73% 6.69 g/L 23.7 g 5.8 gTotal quantity used Liquor Nitren Ni 956 g 23.7 g 5.8 g Filter cake C₁Tare Ni, measured Ni, total 174.4 g 9.68 g/kg  1.67 g  18.00% 28.80%Extract E1 Tare Loss Ni, measured Ni, total 761 g 22.6 g 4.95 g/L  3.88g  79.60%  2.40% 66.90% Difference = −0.25 g Ni = −0.43% of the totalamount of Ni used 1^(st) washing (H₂O) Total amount used corresponds to96.9% of the expressed fibrous material from extract = 1.62 g Ni (sampletaking = 0.05 g Ni loss) Liquor Filter cake C₁ Water 1000.1 g 167.1 g833 g Filter cake C₂ Tare Ni, measured Ni, total 155.2 g 4.34 g/kg  0.67g (15.5%) 11.60% Filtrated material W₁ Tare Loss Ni, measured Ni, total837.6 g  7.3 g 0.51 g/L 0.43 g (83.7%) (0.7%) 7.40% Difference = −0.52 gNi = −8.6% of the total amount of Ni used 2^(nd) washing (H₂O) Totalamount used corresponds to 96.4% of the expressed fibrous material fromthe 1^(st) wash (sample taking = 0025 g Ni loss (93.4% of pulp C₀)Weight of sample Filter cake C₂ Water 894.5 g 149.5 g 745 g Filter cakeC₂ Tare Ni, measured Ni, total 147.9 g 2.49 g 0.37 g (16.6%) 6.40%Filtrated material W₂ Tare Loss Ni, measured Ni, total 741.9 g  4.7 g0.32 g/L 0.24 g (82.9%) (0.5%) 4.15% 3^(rd) washing (0.5% acetic acid)Total amount used corresponds to 95.8% of the expressed fibrous materialfrom the 2^(nd) wash = 0.35 g Ni (sample taking = 0.02 g Ni loss) (89.5%of pulp C₀) Weight of sample Filter cake C₃ 0.5% acetic acid 847.7 g141.7 g 706 g Filter cake C₄ Tare Ni, measured Ni, total 137.4 g 0.37g/kg 51 mg (16.2%)  0.80% Filtrated material W₃ Tare Loss Ni, measuredNi, total 704.8 g  5.5 g 0.48 g/L 0.34 g (83.1%) (0.7%) 5.90% Difference= +0.04 g Ni = +0.6% of the mass of Ni used The total loss of nickel is2.2%.

1. A method to separate hemicelluloses from a hemicellulose-containing biomass, comprising the steps of: a) extracting the hemicelluloses from the hemicellulose-containing biomass by treating the hemicelluloses with a complex compound in aqueous solution and thereby forming a soluble complex of the hemicelluloses, and using as the complex compound a coordination compound from a transition metal and at least one polydentate ligand selected from the group consisting of at least one of tris(2-aminoethyl)amine, ethylene diamine and diethylene triamine, and b) separating the complexed hemicelluloses of step a) from the biomass.
 2. A method according to claim 1, wherein raw pulp is used as the hemicellulose-containing biomass.
 3. A method according to claim 2, wherein the raw pulp used is obtained by delignification of a lignocellulose-containing biomass.
 4. A method according to claim 1, further comprising the step of providing the biomass in a comminuted form.
 5. A method according to claim 1 wherein said transition metal is selected from the group consisting of at least one of nickel, copper, cadmium, cobalt, palladium and zinc.
 6. A method according to claim 1 wherein the complex compound comprises [Ni(tris(2-aminoethyl)amine)(OH)₂].
 7. A method according to claim 1 wherein the complex compound comprises an aqueous solution in a concentration of from about 0.1 to about 10% by weight.
 8. A method according to claim 7 wherein the concentration of the complex compound in the aqueous solution is a concentration of about 1 to 3% by weight.
 9. A method according to claim 1 wherein the extracting step is carried out at a temperature of from about 0° C. to about 90° C.
 10. A method according to claim 9 wherein the extracting step is carried out at a temperature of from about 10° C. to about 80° C.
 11. A method according to claim 10 wherein the extracting step is carried out at a temperature of from about 20° C. to about 40° C.
 12. A method according to claim 11 wherein the extracting step is carried out at a pH value of from about 10 to about
 14. 13. A method according to claim 12 wherein the extracting step is carried out at a pH value of from about 13 to about
 14. 14. A method according to claim 11, wherein the extracting step is carried out for about from 5 mm to about 16 hours.
 15. A method according to claim 14 wherein during the extracting step a liquor ratio in the range of from about 1:3 to about 1:30, is selected.
 16. A method according to claim 15 wherein the extracting step is carried out at a pH value of from about 10 to about
 14. 17. A method according to claim 1, wherein the extracting step is carried out for about from 5 mm to about 16 hours.
 18. A method according to claim 17 wherein the extracting step is carried out for about from 15 minutes to about 2 hours.
 19. A method according to claim 1 wherein during the extracting step a liquor ratio in the range of from about 1:3 to about 1:30, is selected.
 20. A method according to claim 19 wherein during the extracting step, a liquor ratio of from about 1:5 to about 1:20 is selected.
 21. A method according to claim 1 wherein the separating step further comprises separating the complexed hemicelluloses from the remaining biomass by filter presses.
 22. A method according to claim 1 further comprising the step of subjecting the biomass, modified by the method to at least one washing stage.
 23. A method according to claim 22 wherein the transition metal is nickel and further comprising the step of subjecting the biomass, modified by the method to washing with water, for reducing the nickel contents and subsequently with at least one of diluted acid or a complex former for the transition metal.
 24. A method according to claim 1, further comprising the step of treating the complexed hemicelluloses after separation from the biomass to precipitate the hemicelluloses from the solution.
 25. A method according to claim 24 wherein the precipitation of the hemicelluloses is carried out by lowering the pH value to below
 10. 26. A method according to claim 25, further comprising the step of isolating the hemicelluloses after the precipitation.
 27. A method according to claim 25 wherein the precipitation of the hemicellulose is carried out by lowering the pH value to be in the range of between from about 3 to about
 5. 28. A method according to claim 1 wherein the transition metal is nickel and further comprising the step of washing the separated hemicelluloses with an aqueous solution of at least one of ethanol amine, NaOH, ammonia and tris(2-aminoethyl)amine to reduce the nickel content. 